There is hitherto known an in-wheel motor driven automobile including motors and speed reducers that are arranged inside of wheels. In the in-wheel motor driven automobile, when a direction of a torque of each of the motors is reversed, there is a fear in that gear rattling noise may be generated due to a backlash in the speed reducer and be audible to a driver. Patent Literature 1 proposes a technology of reducing the gear rattling noise generated due to the backlash in the speed reducer. An in-wheel motor provided with a speed reducer, which is proposed in Patent Literature 1, includes a motor output shaft to be fitted into a rotor, which is divided into two portions. To each of the two portions of the motor output shaft, an output section including a speed reducer is coupled. One of the output sections includes a first helical gear firmly fixed to the output section and a second helical gear to be brought into meshing engagement with the first helical gear. Another output section includes a third helical gear firmly fixed to the another output section, which is provided so as to be helical in a direction opposite to the first helical gear, and a fourth helical gear to be brought into meshing engagement with the third helical gear. In the in-wheel motor, the second helical gear and the fourth helical gear are fitted over the same output shaft (axel) to transmit a torque to a wheel.
The in-wheel motor described above is configured to reduce the backlash so as to reduce the gear rattling noise generated by the helical gears by shifting a position at which the third helical gear and the fourth helical gear come into meshing engagement with each other in a circumferential direction with respect to a position at which the first helical gear and the second helical gear come into meshing engagement with each other.